In order to protect health and the environment, it is necessary to eliminate undesirable odors and toxic gases from the ventilation air or waste gases occurring as by-products of many manufacturing processes before their discharge to the environment. A known method for removing odors and other organic impurities contained in air or ventilation gases consists in heating the fouled air or gases in a thermal regenerative incinerator system. Such a system which is disclosed by way of example in U.S. Pat. No. 3,870,474, generally comprises at least two and preferably three heat accumulation chambers or regenerators each containing a suitable packing material such as ceramic spheres or nodules, and a combustion chamber positioned to cooperate with both regenerators to effect oxidation of the impurities.
Such an incinerator system has an operating cycle including a plurality of successive steps. In the first step, the waste gases are caused to flow through one of the regenerators in such a manner as to be heated by contact with the packing that has previously been heated, and then to the combustion chamber where total oxidation of the fumes takes place. The hot combustion products are thereafter directed to a second regenerator wherein their heat content is transferred to the packing material. The gases are finally exhausted to the atmosphere. In a second step, the waste gases are directed in the reverse way through the second regenerator, where they are heated. After combustion, they are cooled by passage through the first regenerator and exhausted. Heat losses are made up by injection of auxiliary fuel in the combustion chamber.
In current practice, the incinerator system usually comprises a third regenerator which is added thereto in order to allow for the purging of the waste gases remaining in a regenerator after the waste gas heating period but prior to the introduction of the purified gases.
Regenerative incinerator systems of the above mentioned type are well known apparatuses that have found application for some years for the treatment of waste air or gas streams containing volatile organic compounds in gaseous form, like those produced during the preparation or application of solvent based paints, varnishes or other coatings.
A number of problems arise however when this process is used for the treatment of waste gas or air streams containing condensible organics in the form of aerosols or suspensions of fine liquid particles, like those produced during the impregnation of roofing felts with asphalt base coatings. When treating such waste gases, the condensed vapors or liquid aerosols are carried into the regenerator bed and deposited as a thin liquid film on the inside surfaces of this regenerator and on the packing material in the entrance zone of the regenerator. Upon reversal of the flow, the soiled surfaces are heated by contact with the hot exhaust gases, causing some of the organic liquid film to evaporate and contaminate the otherwise clean gases. This has the effect of materially reducing the destruction efficiency of the process. In addition, any portion of the liquid deposited which is not evaporated remains on the packing and adds up during subsequent cycles, causing a run-off of excess liquid in the gas plenum of the regenerators. This liquid wets the regenerator and packing surfaces and upon evaporation increases the contamination of the exhaust gases. Further, this excess liquid is slowly distilled in contact with the hot gases, leaving behind deposits of tarry substances on the packing and on the walls of the plenum chambers as well as on the valve chambers and moving parts. These deposits can impair the operation of the process and, if allowed to accumulate, can ignite and cause severe overheating and failure of mechanical parts.